Method of producing high Tc superconducting NbN films

Abstract

Thin films of niobium nitride with high superconducting temperature (Tc) of 15.7 DEG K. are deposited on substrates held at room temperature ( DIFFERENCE 90 DEG C.) by heat sink throughout the sputtering process. Films deposited at PAr>12.9+/-0.2 mTorr exhibit higher Tc with increasing PN2,I, with the highest Tc achieved at PN2,I=3.7+/-0.2 mTorr and total sputtering pressure Ptot=16.6+/-0.4. Further increase of N2 injection starts decreasing Tc.

What is claimed is: 
     
       1. A method for forming NbN films having a high T c  in the range of 15° to 16° K. and possessing B1 crystal structure with a (111) texture, without the introduction of carbon or any compound of carbon in any form to obtain the B1 crystal structure and high T c  characteristics, by dc reactive magnetron sputtering niobium on a substrate in a reactive gas mixture of high purity Ar and N 2  and a base pressure of 10 -8  Torr comprising the steps of maintaining said substrate at about 20° C. throughout the sputtering process,   maintaining the partial pressure P N2 ,I of reactive gas, N 2 , constant in a range of 3 to 4 mTorr,   maintaining the partial pressure P Ar  of the carrier gas, Ar, constant in a range of 12.9 to 17 mTorr, and   maintaining the total sputtering pressure constant in a range of 16 to 21 mTorr.   
     
     
       2. A method as defined in claim 1 wherein the dc voltage is set to obtain a constant discharge current of about 1 ampere. 
     
     
       3. A method as defined in claim 2 wherein the surface of the Nb target is precleaned in pure Ar ambient by presputtering the target onto a mechanical shutter which is placed in the sputtering path of said substrate, subsequently after the desired equilibrium of operating parameters is obtained, deposition of the film is initiated by removing the shutter. 
     
     
       4. A method as defined in claim 1 wherein the partial pressure P N2 ,I of reactive gas injection is maintained at 3.7±0.2 mTorr. 
     
     
       5. A method as defined in claim 4 wherein the partial pressure P ar  of the carrier gas is maintained at 12.9±0.2 mTorr. 
     
     
       6. A method as defined in claim 5 wherein the total sputtering pressure is maintained at 16.6±0.4 mTorr.